Ablation catheter with insulation

ABSTRACT

An ablation device and/or method of ablation may include placing one or more ablation electrodes in contact with a target tissue in a lumen. An electrical insulator may be positioned between the electrode and a lumen fluid and an electrical signal (for example a radio frequency signal) may be conveyed between the electrodes to heat and/or ablate the target tissue. Ablation may be bipolar and/or an in lumen disperse electrode may be supplied for unipolar ablation. Ablation progress may be sensed and ablation may be adjusted to produce a desired level and/or geometry of ablation.

RELATED APPLICATION

This application claims the benefit of priority under 35 USC §119(e) ofU.S. Provisional Patent Application No. 61/759,066 filed 31 Jan. 2013,the contents of which are incorporated herein by reference in theirentirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to anablation catheter and, more particularly, but not exclusively, to aradio frequency ablation catheter that may optionally be suited forrenal artery denervation.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided an ablation catheter fitting into a lumen of a patientcomprising: a radially expanding tubular insulation member sized andshaped to fit in a lumen of a blood vessel in an expanded configuration;an expansion mechanism for radially expanding an inner passageway of theradially expanding tubular insulation member toward walls of the bloodvessel, from a retracted configuration to the expanded configuration;and a plurality of ablation electrodes mounted along an outer surface ofthe radially expanding insulation tubular member. In the expandedconfiguration a hydraulic radius of the passageway is at least 50% of ahydraulic radius of the lumen.

According to some embodiments of the invention, the insulator fits intothe lumen which is a blood vessel.

According to some embodiments of the invention, the expansion is byplastic deformation of the insulator.

According to some embodiments of the invention, at least one of theplurality of ablation electrodes is mounted with an active surfacetangent to the outer surface of the expanding tubular insulator theactive surface facing the inner surface of the lumen.

According to some embodiments of the invention, the insulator contactsan area on the inner surface of the lumen. The contact area may surroundat least one of the plurality of ablation electrodes.

According to some embodiments of the invention, the insulator separatesbetween at least one of the plurality of ablation electrodes and fluidin the passageway.

According to some embodiments of the invention, the plurality ablationelectrodes include at least four pairs of ablation electrodes.

According to some embodiments the invention further includes a controlunit selectively conveying an ablation signal between electrodes of eachof the at least four pairs of ablation electrodes.

According to some embodiments the invention further includes adispersive electrode, for conveying a signal to one or more of theablation electrodes.

According to some embodiments the invention further includes theexpansion mechanism includes a plurality of supports.

According to some embodiments the invention further includes theinsulator transfers heat from the plurality of ablation electrodes to aheat sink.

According to some embodiments the invention further includes the heatsink includes the fluid flowing through the lumen.

According to some embodiments the invention further includes the heatsink includes the fluid flowing through the expandable passageway.

According to some embodiments the invention further includes an area ofthe inner surface of the lumen in contact with the insulator surroundingat least one ablation electrode of the plurality of ablation electrodesis at least 50 mm2.

According to some embodiments the invention further includes an area oftarget tissue in contact with the insulator surrounding at least oneablation electrode of the plurality of ablation electrodes includes amargin of at least 3 mm surrounding the at least one electrode.

According to some embodiments the invention further includes in theexpanded configuration a cross sectional area of the passageway is atleast 50% of a cross sectional area of the lumen.

According to some embodiments the invention further includes in theexpanded configuration a hydraulic radius of the passageway is at least70% of a hydraulic radius of the lumen.

According to an aspect of some embodiments of the present inventionthere is provided a method of ablation therapy in a lumen in a patientcomprising: positioning one or more electrodes in contact with a wall ofthe lumen; and expanding an insulator thereby contacting by an outersurface of a wall of the insulator an inner surface of a wall of thelumen; an area of the contacting surrounding at least one of the one ormore electrodes defining by an inner surface of the insulator apassageway along the lumen for flow of a fluid through the lumen, andelectrically insulating between the fluid and the at least one of theelectrodes and heating the tissue by means of an electrical signal fromthe at least one electrode.

According to some embodiments the invention further includes cooling atleast a portion of at least one of the tissue and the electrodesimultaneous to the heating.

According to some embodiments of the invention, the cooling includestransferring heat between the portion and a heat sink.

According to some embodiments of the invention, the transferringincludes conducting heat across the wall of the insulator.

According to some embodiments of the invention, the heat sink includesthe fluid in the lumen.

According to some embodiments of the invention, the heat sink includesfluid in the passageway.

According to some embodiments of the invention, the passageway passesalong a surface of the insulator opposite an ablation zone.

According to some embodiments of the invention, the contacting includescontacting an area of the inner surface of the wall of the lumensurrounding the electrode.

According to some embodiments of the invention, the area of the innersurface of the wall of the lumen surrounding the electrode includes anarea of at least 50 mm2.

According to some embodiments of the invention, the contacting includesa margin around the electrode of at least 3 mm in every direction.

According to an aspect of some embodiments of the present inventionthere is provided an ablation catheter comprising: a plurality ofablation electrodes in contact with a target tissue in a lumen; adispersive electrode provided in the lumen, the dispersive electrodehaving a conducting contact area at least 20 times a large as theablation electrode, and a control unit conveying a first signal betweena pair of the plurality of ablation electrodes and a second signalbetween the dispersive electrode and at least one of the plurality ofablation electrodes.

According to some embodiments the invention further includes aninsulator electrically insulating at least one of the ablationelectrodes from a fluid in the lumen.

According to some embodiments the invention the dispersive electrode isnot in contact with the target tissue.

According to some embodiments the invention further includes apassageway for a fluid to pass through the lumen.

According to some embodiments the invention a first side of theinsulator is in contact with the target tissue in a vicinity of theablation electrode and a second side of the insulator is in contact withthe fluid in the passageway and heat transfer to the fluid across theinsulator cools the target tissue in the vicinity of the ablationelectrode.

According to some embodiments the invention the dispersive electrode isin contact with a fluid inside the lumen.

According to an aspect of some embodiments of the present inventionthere is provided a method of ablation therapy inside a lumen of apatient comprising: positioning a plurality of ablation electrodes incontact with a target tissue in the lumen; conveying through the targettissue a first electrical signal between a pair of the ablationelectrodes; and conveying through the target tissue a second electricalsignal between at least one of the plurality of ablation electrodes andthe a dispersive electrode having an active surface area at least twentytimes an active surface area of the ablation electrode.

According to some embodiments the invention further includes insulatingelectrically at least one of the ablation electrodes from a fluid in thelumen.

According to some embodiments the invention further includes placing thedispersive electrode into contact with a fluid in the lumen.

According to some embodiments the invention further includes placing atleast part of the dispersive electrode into the lumen.

According to some embodiments the invention the placing is by means of acatheter.

According to an aspect of some embodiments of the present inventionthere is provided at least one ablation electrode in contact with atissue on an inner wall of a lumen; an insulator including a tissue sidein contact with an area of the tissue surrounding the electrode and alumen side in contact with fluid in the lumen, the insulatorelectrically insulating the at least one ablation electrode from a fluidin the lumen; and a passageway allowing fluid flow through the lumen.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a flowchart illustrating a method of ablation in accordancewith some embodiments of the present invention;

FIG. 2 is a flowchart illustrating a method of bipolar ablation inaccordance with some embodiments of the present invention;

FIG. 3 is a flowchart illustrating a method of unipolar ablation inaccordance with some embodiments of the present invention;

FIGS. 4A-D are illustration of an ablation device in accordance withsome embodiments of the present invention;

FIG. 5 illustrates a windsock type insulator in accordance with someembodiments of the present invention;

FIGS. 6A-B illustrate a laser-cut tube type support structure inaccordance with some embodiments of the present invention;

FIG. 7 is an illustration of a support structure formed of spiral wirein accordance with some embodiments of the present invention;

FIG. 8 is a an illustration of an insulating frame in accordance withsome embodiments of the present invention;

FIGS. 9A-B illustrate a support structure and insulator in accordancewith some embodiments of the present invention;

FIG. 10 illustrates a laser-cut tube support structure and insulator inaccordance with some embodiments of the present invention;

FIGS. 11A-B illustrate a laminar support structure in accordance withsome embodiments of the present invention;

FIGS. 12A-B illustrate a support structure including braided wires inaccordance with some embodiments of the present invention;

FIGS. 13A-C illustrate a support structure including a break out malecotin accordance with some embodiments of the present invention;

FIGS. 14A-C illustrate a support a distal-extending malecot inaccordance with some embodiments of the present invention;

FIGS. 15A-B illustrate a hydraulic support structure in accordance withsome embodiments of the present invention;

FIGS. 16A-C illustrate a printed circuit board support structure andinsulator in accordance with some embodiments of the present invention;

FIG. 17 illustrates control unit in accordance with some embodiments ofthe present invention;

FIG. 18 is a flow chart illustration of a method of ablation and/ormeasuring evoked response in accordance with some embodiments of thepresent invention;

FIG. 19 illustrates simulated measurements of an evoked response inaccordance with some embodiments of the present invention;

FIG. 20 illustrates a ablation device included sensors for evokedresponse in accordance with some embodiments of the present invention;and

FIGS. 21A-B illustrate an alternate ablation device included sensors forevoked response in accordance with some embodiments of the presentinvention;

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to anablation catheter and, more particularly, but not exclusively, to aradio frequency (‘RF’) ablation catheter that may optionally be used forrenal artery denervation.

In some embodiments, the present invention relates to methods and/ordevices (e.g., control unit) for ablation using ablation catheter, e.g.,RF ablation catheter.

Overview

1 Ablation Device with Electrical Insulation and Cooling

An aspect of some embodiments of the current invention relates to amethod of catheter ablation wherein an ablation electrode is optionallyintroduced into a lumen and/or positioned in contact with a tissue to beablated. For example the tissue may be part of the inner surface of thelumen. The ablation catheter may be provided with an insulator, forexample a polyurethane membrane. In some embodiments the insulator maybe tubular. For the sake of the current application a tubular insulatormay have insulating wall surrounding one or more passageways. The walland the passageways may have a non-circular cross section. The crosssection may change along the length (for example to fit a changing crosssection of lumen in a patient). A tubular insulator may be elongated(the axis may be greater than the width) or short (the axis may shorterthan the width). An outer surface of the insulator may be optionallypressed against tissue surrounding the location of the ablationelectrode. The membrane may for example electrically insulate theablation electrode and/or an ablation zone from a fluid in the lumen.The ablation zone may be heated and/or ablated by conveying anelectrical signal (for example an RF signal) between the ablationelectrode and a second electrode. A portion of the ablation zone mayoptionally be cooled. For example the insulator may transfer heat awayfrom the electrode and/or the lesion formed by the ablation and/or thetissue in the vicinity of the electrode and/or tissue in the vicinity ofthe lesion. Optionally, the insulator may conduct the heat to a heatsink. For example a heat sink may include a fluid. The fluid may be incontact with the inner surface of the insulator that is opposite theablation zone. For example the heat sink may include lumen fluid (forexample blood) flowing across the inner surface of the insulatoropposite the ablation zone and/or an artificial cooling fluid. The localthickness and/or heat conductivity of the insulator may optionally beadjusted to preferentially cool one portion of the ablation zone morethan another portion.

In some embodiments, the insulator may optionally be pressed against theinner wall of the lumen and/or expanded by supports that open like atent and/or an umbrella and/or an expandable basket and/or a malecot.The support structure may optionally include for example ribs and/orstretchers like an umbrella and/or other support (e.g., brace, buttress,stanchion, cantilever, strut, frame and/or spines). The supports mayinclude, for example, inflatable (hydraulic and/or pneumatic) supports,supports made of nitinol, a folding basket, a malecot, a stent, afolding stent, a laminated structure, a balloon and/or an expandablewoven structure. The insulator may allow fluid flow through the lumen.For example, the insulator may be open at a distal end, allowing bloodto continue to flow through the delivery vessel. For example, theinsulator may include a passageway to allow flow past the insulator. Forexample the insulator may have an open ended tubular geometry. Fluid mayoptionally flow along the lumen through a passageway along the axis of atubular insulator while the insulator walls insulate the inner surfaceof the lumen from the fluid. Optionally, the insulator may be expandedto fill the lumen. Optionally, as the insulator expands, the passagewaymay also expand. For example the passageway may have a cross sectionopen to flow that has an area of least 50% of the area of the crosssection of the lumen that is open to flow. Alternatively or additionallythe hydraulic radius of the passageway (defined for example as the fourtimes cross sectional area divided by the wetted perimeter) by may be70% of the hydraulic radius of the lumen. In some embodiments the crosssectional area of flow the passageway may range between 25% and 50% ofthe cross sectional area of flow in the lumen and/or the hydraulicradius of the pathway way may range between 50% and 70% of the hydraulicradius of the lumen.

The expanding tent, basket and/or umbrella structure may for examplehave a expanded width ranging for example between 4 and 8 mm and/orranging for example between 1 and 10 mm. The length of the basket, tentand/or umbrella structure may for example range between 10 and 40 mmand/or between 20 and 30 mm. optionally, in its expanded configurationthe insulator may be spread against all wall of the lumen.

For example, the insulator may include a membrane of thickness rangingbetween for example 0.1 and 0.01 mm and/or may pose impedance (againstisoconductive saline solution) for example ranging between 50 to 150 kΩat 460 kHz (e.g., 50 to 100 kΩ, 100 to 150 kΩ etc.). The membrane may bemade from, for example, Urethane and/or a polyurethane polymer. In someembodiments, the basket may have a diameter of less than 6 French (2 mm)when out of an intravascular delivery sheath but before expanding. Insome embodiments, the basket may contract to a diameter of less than 6French (2 mm) contracted but before being reinserted into the sheaththat is commonly used to introduce a catheter to its intended deliverylocation within the vasculature.

2 General

Some embodiments of the current invention may include a multi-electrodeablation device. The device may be inserted into a body lumen via acatheter. At times the ablation device may be referred to as an ablationcatheter or a catheter. A multi-electrode ablation catheter may bepowered by a control unit (e.g., including an RF generator). The controlunit may have a number of channels that convey an electrical signalbipolarly (for example from a first ablation electrode in contact withthe target tissue at a first location to a second ablation electrode incontact with the target tissue at a second location) through a targettissue between electrode pairs (for example, the ablation electrodes maybe mounted on the catheter's working [distal] end), and/or unipolarlythrough a target tissue between an ablation electrode (that mayoptionally be in contact with the target tissue) and a dispersive(reference) electrode (e.g., a shaft electrode in contact with lumenfluid (for example blood) and/or an external electrode). The electrodesmay be activated in accordance with a switch configuration set by amultiplexer. Multiplexer RF channels may be used to transmit radiofrequency (RF) ablation energy to the electrodes. The RF channels mayoptionally include means to measure electrode/tissue impedance. In someembodiments, measurements may be made with high accuracy and/orrepeatability. The RF channels may optionally be controlled by acontroller (e.g., a microcontroller and/or single-board computer).

Optionally a catheter according to some embodiments of the currentinvention may be used for renal denervation. Renal denervation, is aminimally invasive, endovascular catheter based procedure usingradiofrequency ablation aimed at treating resistant hypertension.Radiofrequency pulses may be applied to the renal arteries. Ablation insome embodiments may denude nerves in the vascular wall (adventitialayer) of nerve endings. This may causes reduction of renal sympatheticafferent and efferent activity and/or blood pressure can be decreased.During the procedure, a steerable catheter with a radio frequency (RF)energy electrode tip may deliver RF energy to a renal artery viastandard femoral artery access. A series of ablations may be deliveredalong each renal artery.

As used herein, the term “controller” may include an electric circuitthat performs a logic operation on input or inputs. For example, such acontroller may include one or more integrated circuits, microchips,microcontrollers, microprocessors, all or part of a central processingunit (CPU), graphics processing unit (GPU), digital signal processors(DSP), field-programmable gate array (FPGA) or other circuit suitablefor executing instructions or performing logic operations. Theinstructions executed by the controller may, for example, be pre-loadedinto the controller or may be stored in a separate memory unit such as aRAM, a ROM, a hard disk, an optical disk, a magnetic medium, a flashmemory, other permanent, fixed, or volatile memory, or any othermechanism capable of storing instructions for the controller. Thecontroller may be customized for a particular use, or can be configuredfor general-purpose use and can perform different functions by executingdifferent software.

The controller may optionally be able to calculate the temperature ofsome or all of the electrodes and/or near some or all of the electrodes.For example, temperature measurements may be sensed by means of thethermocouple attached to each electrode and the output of the means isforwarded to the controller for calculation. Interaction with the user(e.g., a physician performing the ablation procedure) may optionally bevia a graphical user interface (GUI) presented on for example a touchscreen or another display.

In some embodiments, electrode impedance measurements may be used toestimate contact (estimated contact) between electrode and tissue assurrogate for thermal contact between electrode interface and targettissue. In some embodiments, power being converted to heat atelectrode/tissue interface may be estimated (estimated power) forexample based on the estimated contact, applied power and/or electrodetemperature. Together with the time of RF application to the tissue, theestimated contact and/or estimated power and/or electrode temperaturemay optionally be used to calculate energy transferred to target tissueand/or resulting target tissue temperature locally at individualablation electrode locations. Optionally, the results may be reported inreal-time. Optionally, based for example on the calculated cumulativeenergy transferred to target tissue, the duration of ablation may becontrolled to achieve quality of lesion formation and/or avoidundesirable local over-ablation and/or overheating. Control algorithmsmay deem to have completed lesion formation successfully for examplewhen the quality of lesion at each electrode location reaches apredetermined range.

Some embodiments of the current invention may combine a multi-electrodeablation device with blood exclusion. In some embodiments, the distancefrom the proximal end of the insulating basket to the distal end (towardthe catheter tip) of an in-catheter dispersive electrode may range forexample between 10 to 75 mm (e.g., between 10 to 15 mm, between 10 to 25mm, between 25 to 50 mm, between 50 to 75 mm etc.). For renal arterydenervation, the distance between the dispersive electrode and theproximal end of the expandable structure may range preferably between 20to 50 mm (e.g., 20 mm, 30 mm, 40 mm, 50 mm etc.) to ensure that thedispersive electrode is within the aorta, and away from the desiredablation area within the renal artery.

Various embodiments of the current invention may be configured to fitfor example in a 5 French (1.33 mm diameter) catheter with a lumenextending from the handle through the distal tip making it possible toinsert it with the aid of a standard 0.014 inch (0.36 mm) guide wire.The flexibility of the assembly may optionally be compatible withapplicable medical standards. A catheter (for example the variousembodiments described below) may include a guidewire. For example, theguidewire may be inserted through a lumen of the catheter. Optionally,the guidewire may help position the catheter. The guidewire mayoptionally be able to extend past an orifice at the distal end of thecatheter.

3 Bipolar and Unipolar Ablation

An aspect of some embodiments of the current invention relates to amethod of catheter ablation using bipolar and/or unipolar ablation,e.g., to achieve a desired lesion geometry. For example, bipolarablation between a first and a second ablation electrode may be used toconvey an electrical signal through a target tissue to produce a lesion.Ablation may progress more quickly at the location of the firstelectrode than at the location of the second electrode. Bipolar ablationmay optionally be paused and unipolar ablation may be initiated betweenthe second ablation electrode and a dispersive electrode to increaseprogress of ablation in the vicinity of the second electrode. A balanceof unipolar and/or bipolar ablation may be used to adjust a geometry ofa lesion. For example, bipolar ablation may be used to achieve spreadingof a lesion along a tissue surface. For example, unipolar ablation maybe used to deepen a lesion.

In some cases it may be desired to ablate tissue in a given area to aneffective level (for example effective ablation may occur for heating toa temperature of between 60° and 70° C. for a time between 20 and 180sec.). Tissue and/or contact with electrodes may be heterogeneous.Tissue may heat and/or ablate unevenly. Overheating and/or over-ablatingtissue may have serious consequences (for example heating to over 90° C.and/or over-ablating may cause blood coagulation and/or blood clotsand/or damage to arteries and/or internal bleeding etc.). In someembodiments, the current invention may facilitate monitoring and/orcontrol of ablation within parts of a lesion. In some embodiments, localmonitoring and/or control may produce more even ablation. For example adesired level of ablation may be reached in multiple regions of a lesionwithout over ablating any region.

4 In-Lumen Dispersive Electrode

An aspect of some embodiments of the current invention relates to anin-lumen dispersive electrode for unipolar ablation. The dispersiveelectrode may be introduced into a body lumen and/or electrical contactmay be supplied by a fluid in the lumen. The dispersive electrode may beinserted into the same lumen as an ablation electrode. The dispersiveelectrode may be part of the same catheter as an ablation electrode.Optionally, a single catheter may include a dispersive electrode and aplurality of ablation electrodes. The catheter and/or electrodes may beconfigured to operate in unipolar and/or bipolar modes.

In some embodiments, a control unit may supply power for ablation (forexample: a radio frequency (RF) generator). For example the control unitmay be a rechargeable and/or battery-powered. The ablation generator mayoperate for example around the 460 kHz frequency and/or ranging forexample between 400 and 600 kHz or other RF frequency ranges assigned toISM (Industrial, Scientific, and Medical) applications within thelow-frequency (LF: 30 to 300 kHz), medium-frequency (300 kHz to 3 MHz),and high-frequency (HF 3 to 30 MHz) portions of the RF spectrum. Thecontrol unit may have a number of channels that allow ablation to beconducted bipolarly between electrode pairs through the target tissue.The generator may optionally be able to deliver ablation energy to beconveyed simultaneously between one, some and/or all bipolar ablationelectrode pairs in the catheter. For example a catheter may include fouror more bipolar ablation electrode pairs. In some embodiments, thegenerator may supply a maximum power of, for example, between 3-10 W perbipolar channel. The generator may optionally be able to ablateunipolarly between one, some and/or all of the contact electrodes and adispersive electrode, e.g., catheter-borne reference in-lumen dispersiveelectrode. Lesion formation may for example take between 15 to 180seconds. Each channel may have a minimum voltage compliance of 100 V. Insome embodiments, the minimum voltage compliance may permit, forexample, an average of between 2 and 10 W to be delivered per bipolarelectrode pair presenting an impedance for example ranging between 1.0and 1.5 kΩ.

In some embodiments, an ablation electrode of the current invention maybe made for example of between 80% and 95% Platinum and/or between 20%and 5% Iridium. The ablation electrodes may range for example between0.5 and 4 mm long and/or have an electrically active area for example ofbetween 0.1 and 1 mm² and/or have a diameter ranging from 0.01 to 0.05inch (0.25 to 1.27 mm). The electrically active area of the ablationelectrodes may be in contact with a target tissue. The distance betweenablation electrodes may range for example between 0.5 and 3 mm or more.

In some embodiments, a dispersive electrode may for example have alength ranging for example between 4 to 20 mm and/or have a diameterranging between 2 and 5 French (between 0.67 and 1.67 mm). Thedispersive electrode may have an electrically active area ranging forexample, 20 to 50 times or more than the electrically active area and/orsurface of contact of the ablation electrodes. For example theelectrically active area of the dispersive electrode may range between50 to 150 mm² (e.g., between 50 to 100 mm2, between 100 to 150 mm2,between 75 to 120 mm2 etc.). Optionally the electrically active surfaceof the disperse electrode may be in electrical contact with a fluid in alumen of a patient. In some embodiments, the dispersive electrode may becoated with a material such as porous titanium nitride (TiN) or iridiumoxide (IrOx). The coating may increase microscopic surface area of theelectrode in electrical contact with lumen fluid.

5 Local Measurement of Ablation Progress

An aspect of some embodiments of the current invention relates to amethod of catheter ablation wherein ablation progress may be measuredlocally at the site of one, some and/or all ablation electrodes. Forexample, during a pause in the bipolar ablation signal, impedance may bemeasured locally at an ablation electrode for example by measuringimpedance between the ablation electrode and a dispersive electrode.

For example, the system may measure the complex bipolar and unipolarelectrode impedance at the ablation frequency. Optionally when notablating, an auxiliary signal may include an auxiliary current not meantto cause significant physiological effect. Electrode Impedancemeasurements may optionally be possible within the 100Ω to 1 kΩ rangewithin a minimum accuracy ranging for example between 2 to 10%, andwithin the 100Ω to 2 kΩ range with a minimum accuracy ranging forexample between 5 to 20%. Minimum repeatability within the 100Ω to 2 kΩrange may range for example between 2 to 10%. Ablation interruptions mayrange from 1 to 100 ms when measuring unipolar impedance during bipolarablation segments. Impedance measurements may be taken at a minimum rateranging for example between 50 to 200 samples for use by the controlalgorithm.

In some embodiments, temperature may be measured individually at one,some and/or all of the contact electrodes. Temperature measurements mayuse, for example, a thermocouple. The thermocouple may optionally beformed between the main electrode's wire and an auxiliary thermocouplewire. Temperature measurement range may be for example between 30° C. to100° C. or more. Temperature measurement accuracy range between ±0.2 to±1° C. or may be more accurate. Temperature measurement repeatabilitymay range for example between 0.1 to 0.5° C. or less. Targettemperatures may range for example between 60 to 80° C.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

Exemplary Embodiments 1 Outline of Method of Ablation

Referring now to the drawings, FIG. 1 is a flow chart illustration of amethod of therapy using unipolar and/or bipolar ablation, in accordancewith some embodiments of the invention. The exemplary method,illustrated for example in FIG. 1, of unipolar and bipolar ablation maybe used to achieve a desired lesion geometry, to measure the progress ofablation locally near electrodes and/or in an area between electrodesand/or to adjust a geometry of a lesion. The method may be used tocontrol power and duration of ablation at one or more electrodes, e.g.,to ensure quality of lesion formation.

In some embodiments, an ablation device may be set up 101. In someembodiments, a catheter with the ablation device may be inserted 102into a patient. A dispersive electrode may optionally be placed 104 incontact with a large area of the patient. Optionally, the dispersiveelectrode may be inserted into the patient with the catheter (e.g., thedispersive electrode may be part of the catheter). Alternatively oradditionally the dispersive electrode may be independent of thecatheter. The large contact area, for example the contact area may rangebetween 50 to 150 cm² or more of the dispersive electrode may reducetissue damage and/or impedance in the vicinity of the dispersiveelectrode.

In some embodiments, a two or more ablation electrodes may be positioned106 in contact with a target tissue in an area to be ablated. Theablation electrodes may have a small contact area with the targettissue. Current flowing from the ablation electrode may be concentratedin the small contact area causing local ablation. The high currentflowing through a small contact area in the vicinity of the ablationelectrode may produce a high electrical impedance in the vicinity of theablation electrode. For example, most of the impedance for currentbetween the dispersive electrode and the ablation electrode may occur inthe vicinity of the ablation electrode.

The ablation device may optionally include an insulator. The insulatormay optionally be expanded 107 and/or spread 108 across a surface of atarget tissue. Optionally, the insulator may isolate the electrode froma fluid in a lumen (for example blood in an artery). Optionally, theinsulator may prevent leaking and/or or shunting of ablative energy awayfrom a target.

In some embodiments, after positions 106 the ablation electrodes and/orexpanding 107 and/or spreading 108 the insulator, the contact of theablation electrodes with the target tissue may be tested 109. Forexample, the impedance may be measured between the ablation electrodeand the dispersive electrode and/or the temperature may be tested at theablation electrode while applying current. If the contact is not good110 (Step 110: no) (for example the impendence is high) then theablation electrode may be repositioned (for example by re-inserting 102the catheter and/or moving and/or re-positioning 106 the ablationelectrodes).

In some embodiments, once the ablation electrodes are proper positionedand/or contact is good 110 (Step 110: yes), ablation may proceed. Forexample, bipolar ablation 112 may take place between two ablationelectrodes (note as used herein bipolar ablation may also includemultipolar ablation between more than two ablation electrodes). Optionaldetails of bipolar ablation 112 are described, for example, in FIG. 2.In some embodiments, unipolar ablation 114 may take place between one ormore ablation electrodes and a dispersive reference electrode. Forexample, if during bipolar ablation 112 it is observed that ablation isproceeding faster near one of the ablation electrodes than near theother electrode of the pair and/or that one electrode is heating up toomuch and/or that ablation is taking place too near the surface etc.,bipolar ablation 112 may be interrupted (for example not passing currentand/or passing a reduced current) and/or optionally the fast and/oroverheating electrode may be allowed to rest (for example not passingcurrent or passing a reduced current). Unipolar ablation 114 mayoptionally continue at all or some of the electrodes. One or more roundsof bipolar ablation 112 and/or rest and/or unipolar ablation 114 maycontinue (Step 115: no) until the ablation is finished (Step 115: yes).When ablation is finished at a given location, the process may berepeated at another location 116.

2 Bipolar Ablation

FIG. 2 is a flow chart illustration of a method of bipolar ablation inaccordance with some embodiments of the current invention. Bipolarablation 112 may optionally start after prior processes 201 asillustrated for example in FIG. 1. Bipolar (or multipolar) ablation 112may proceed by applying a high current 220, e.g., resulting in thedesired power delivered to the tissue, for example, an average ofbetween 2 and 10 W (e.g., 2 W, 4 W, 5 W, 10 W etc.) between one or morepairs of ablation electrodes. During the application of current 220, thetemperature at one, some or all of the ablation electrodes and/or thecurrent and/or the impedance between pairs of electrodes may optionallybe monitored. Application of current may continue for example between5-200 milliseconds (e.g., 50-200 milliseconds, 100-200 milliseconds,150-200 milliseconds etc.) at a power ranging for example between 2.0 to10 WATT between each pair of ablation electrodes. Current applicationmay be interrupted 221 for a short period, for example between 50-200milliseconds at which time impedance and/or temperature may be tested222 at the location of one or more of the ablation electrodes and/orother locations. For example, impedance may be tested 222 by applying asmall current between the ablation electrode and a dispersive electrode.After testing 222, application 220 of current may optionally continue(for example as long as bipolar ablation 112 has not been completed(step 224 “no”) and/or if there are no signs of overheating and/orover-ablation). The interruption of current application 220 mayoptionally be short enough that the target tissue does not significantlycool and/or ablation is not adversely affected. Optionally, when bipolarablation 112 at a particular location is completed (step 224 yes), forexample it reaches a desired level and/or ablation and/or temperature ata location reaches a safety limit, bipolar ablation 112 at that locationmay stop. Completion 224 of a lesion may, for example may be evaluatedby a “quality of lesion formula” which may be some function ofimpedance, temperature, and energy delivered. The total length of thebipolar ablation 112 at a single location may range for example between15-300 sec. Bipolar ablation may continue at other locations and/or anext process 214 may start.

3 Unipolar Ablation

FIG. 3 is a flow chart illustration of a method of unipolar ablation inaccordance with some embodiments of the current invention. Unipolarablation may be performed by passing current between for example anablation electrode (e.g., an ablation electrode of a pair) and adispersive electrode. Optionally, the dispersive electrode may have alarge area of contact with the patient. Typically the majority of theimpedance and/or ablation occurs at the location and/or near theablation electrode. Sometimes, unipolar ablation may cause deeperlesions than bipolar ablation. In some embodiments, unipolar ablationmay be used to preferentially ablate tissue at a single location and/orto achieve preferred ablation geometry, for example to achieve a deeperlesion.

Unipolar ablation may optionally follow after a previous process 312.For example, after bipolar ablation achieves a large and/or shallowand/or heterogeneous lesion, unipolar ablation may be used to ablate asmall area and/or to achieve a deeper lesion and/or even out a lesion(for example to ablate a portion of a less well done portion of alesion).

Unipolar ablation 114 may proceed by applying a high current 320, e.g.,resulting in the desired power delivered to the tissue, for example, anaverage of between 2 and 10 W (e.g., 2 W, 4 W, 5 W, 10 W etc.) betweenone or more ablation electrodes and a dispersive electrode. During theapplication of current 320, the temperature at one, some or all of theablation electrodes and/or the current and/or the impedance between theelectrodes (e.g., an ablation electrode and dispersive electrode) mayoptionally be monitored. Application of current may continue for examplebetween 50-200 milliseconds and/or between 200 milliseconds and 20seconds and/or between 20 seconds and 200 seconds at a power of 0.5-10WATT between each ablation electrode and the dispersive electrode. Highcurrent application may be interrupted for a short period for examplebetween 0.5-100 milliseconds at which time impedance and/or temperaturemay be tested 322 at the location of one or more of the ablationelectrodes and/or other locations. For example, testing 322 may includemeasuring local impedance for example by applying a small currentbetween one of the ablation electrodes and the dispersive electrode.Alternatively or additionally testing 322 may include calculating a“quality of lesion”. After testing 322, application 320 of current mayoptionally be resumed (step 324 no) (for example if local ablation hasnot been completed and/or if there are no signs of local overheatingand/or over-ablation). The interruption of current application 320 mayoptionally be short enough that the target tissue does not significantlycool and/or ablation is not adversely affected.

In some embodiments, when ablation at a particular location reaches adesired level and/or ablation and/or temperature at a location reaches asafety limit (step 324 yes) unipolar ablation 114 at that location maybe stopped. Unipolar ablation 114 may continue at other locations orother ablation electrodes and/or a next process 316 may start. Forexample, bipolar ablation may proceed between two electrodes untilablation reached a desired limit and/or a safety limit (step 324 yes) atsome location (for example ablation may reach a limit near a first oftwo electrodes). Bipolar ablation may be stopped. Ablation mayoptionally be continued at the second of the two electrodes. Forexample, unipolar ablation may be used in order to “touch up” theablation at each site of the second electrode. Alternatively oradditionally, bipolar ablation may continue between the second electrodeand another electrode for example as described herein below.

4 Exemplary Ablation Devices

FIGS. 4A-16C illustrate various embodiments of ablation devices and/orinsulators in accordance with some embodiments of the current invention.An ablation device may optionally include an insulator, for example theinsulator may include a membrane and/or a frame. The membrane mayoptionally have a tubular form. In some embodiments, the insulator outersurface of the insulator may optionally be pressed against an innersurface of a wall of a lumen or vessel in the vicinity of an ablationtarget and or in an area surrounding an electrode. For example theinsulator may exclude lumen fluid from an area on the inner wall of thelumen ranging between 0.1 mm² and 40 mm² around one or more electrodes.Optionally the insulator may electrically isolate the electrode and/orthe area of tissue surrounding the electrode from the lumen fluid. Insome embodiments, expansion of a support structure may press aninsulator against an inner wall of a lumen.

FIGS. 4A-C illustrates a schematic view of an exemplary ablation device400, in accordance with some embodiments of the current invention. Insome embodiments, an ablation catheter may be inserted into a lumenand/or opened to contact a target tissue. The ablation device mayinclude an insulator that may optionally prevent shunting of ablationenergy away from a target tissue and/or may cool a portion of theablation zone. For example, the insulator may transfer heat to a heatsink. For example, heat transfer may be by conduction. For example theheat sink may include fluid to flowing past the ablation zone cooling asurface of the insulator opposite the ablation zone. Optionally, ahighly heat conductive material (for example metal) may be added to theinsulator in a certain location to preferentially cool that locationand/or the insulator may be made thinner in a particular location toallow more heat conduction away from that location. In some embodiments,the ablation catheter may include a dispersive electrode with largesurface area. The dispersive electrode may provide a unipolar reference.The dispersive electrode may optionally be inserted into the lumen withthe ablation electrodes. Optionally, the dispersive electrode may be inelectrical contact with fluid (for example blood) within the lumen. Forexample, the dispersive electrode may surround the ablation catheter'sshaft.

Some embodiments of an ablation device may optionally include a tubularinsulator. For example, an insulator may include a membrane 434 that hasan tubular form. Membrane 434 may optionally be expanded and/or spreadagainst a target tissue, for example an inner surface of a lumen.Membrane 434 may optionally prevent shunting of ablation energy awayfrom the target tissue. For example, membrane 434 may optionally preventshunting of ablation energy into a fluid (for example, blood) invicinity of an ablation electrode 436. In some embodiments, an ablationelectrode 436 may optionally be coated with a non-electricallyconductive material 435 except for the segment that protrudes throughthe blood-exclusion membrane to contact the target tissue. In someembodiments, decreasing shunting may decrease the power necessary forablation and/or increase the control and/or precision of measurement ofthe power applied to the target tissue.

Membrane 434 may optionally allow fluid to flow 439 (for example seeFIG. 4B) along the lumen. For example, membrane 434 may have a tubularform allowing fluid flow 439 along a passageway 477 along the axis ofthe insulator. Membrane 434 may be thin taking only a small portion ofthe cross section of the lumen. Passageway 477 may optionally includemore than half the cross section of the lumen. The hydraulic radius ofpassageway may be more than 70% of the hydraulic radius of the lumen.Membrane 434 may optionally transfer heat away from the ablation zone.For example membrane 434 may conduct heat to fluid flowing 439 inpassageway 477. For example, blood flow 439 across the inside surface ofthe insulator (opposite the target tissue) may cool the outside surfacethat is against the target tissue and/or a portion of the target tissue.By cooling the target tissue, the lesion may be made deeper and/or moreeven (as has been observed for example in irrigated ablationprocedures). Alternatively or additionally, blood flow 439 across theinside surface of the insulator may cool electrodes 436. Reducing thetemperature of the electrode may reduce the temperature in the interfacebetween electrode 436 and the tissue. Reducing the temperature at thetissue electrode interface may allow more power to be delivered deeperinto the tissue. Alternatively or additionally, allowing fluid flow 439in the lumen may reduce pain and/or secondary tissue damage due toblockage of circulation during the ablation procedure.

In some embodiments, an ablation device may include one or more markers.For example, device 400 includes two individually recognizable radioopaque markers 455 a,b. Markers 455 a,b may optionally be easilyrecognized in radiographic and/or other extra body images (for examplean image may be made using ultrasound and/or magnetic resonance MRIand/or x-ray and/or other imaging techniques). Distinguishing markers455 a,b may help a clinician locate and/or determine the orientation ofa catheter and/or a support structure and/or individual electrodes 436.

In some embodiments, a guidewire 442 may be inserted through a lumen ofthe catheter. For example, guidewire 442 may help position the catheter.Guidewire 442 may optionally be able to extend past an orifice 445 atthe distal end of the catheter.

In some embodiments, a dispersive electrode 440 may be inserted into alumen in the patient being treated. For example, in device 400,dispersive electrode 440 may be inserted into the same lumen as ablationelectrodes 436. Dispersive electrode 440 may optionally have a largesurface of contact. For example, dispersive electrode 440 may be incontact with fluid inside the lumen. The large contact area may decreaselocal impedance and/or heating near dispersive electrode 440. Dispersiveelectrode 440 may optionally be coated with a material such as poroustitanium nitride (TiN) or iridium oxide (IrOx) for example to increaseits microscopic surface area in electrical contact with the fluid.

Ablation device 400 may include, for example a plurality of ablationelectrodes 436. Ablation electrodes may optionally be used in pairs forbipolar ablation. Optionally a signal may be transmitted between any twoelectrodes 436. Dispersive electrode 440 may be used for example to passa high current to one, some or all of the ablation electrodes to performunipolar ablation. Dispersive electrode 440 may optionally be used formeasuring the local impedance near one or more of the ablationelectrodes 436. For example a small current may be passed betweendispersive electrode 440 and one of the ablation electrodes 436 to testimpedance in the local area of the ablation electrode 436. An optionalmultiplexed power source 441 (e.g., current source) (for example seeFIG. 4B) may be used to supply current to a selected group of electrodes(for example including some or all of ablation electrodes 436 and/ordispersive electrode 440) during a time slice and/or a different groupof electrodes (for example including some or all of ablation electrodes436 and/or dispersive electrode 440) during a different time slice.

For example, ablation device 400 may optionally include a “basket” madeout of nitinol wire spines and/or supports 432. Ablation electrodes 436may optionally be positioned on supports 432. For example pairs ofablation electrodes 436 may be distributed along the periphery of thebasket to ablate the intrabody target tissue. Optionally, each electrodemay be fitted with a thermocouple and/or other suitable sensor.

For example, an insulator may include a polyurethane membrane 434.Membrane 434 may be is placed onto the supports 432. Upon deployment,the basket including supports 432 and/or membrane 434 may optionallyopen up like an umbrella. In the exemplary embodiment, ablationelectrodes 436 may optionally be exposed to target tissue on the innerwalls of the lumen into which the catheter is deployed.

The insulator may optionally include non-porous membrane 434 coveringthe mid-section of the expandable basket structure. The membrane mayoptionally separate blood from the treatment area. Membrane 434 mayoptionally increase the portion of electrical ablation energy deliveredto the target tissue for example by reducing the shunting of theablation energy to the blood. In contrast to some occluding means toexclude blood (for example balloons), the basket and/or membrane 434 maybe open at the distal and/or proximal ends, allowing blood to continueto flow 439 through the lumen (for example the delivery vessel and/orartery). During the ablation procedure tissue and/or organs may continueto receive blood. During the ablation procedure blood passing along theinside surface of membrane 434 may cool the surface of the targettissue.

In some embodiments, an ablation catheter may include a plurality ofablation electrode pairs. For example ablation device 400 may includefour pairs of ablation electrodes 436 helically distributed around anopen tubular basket near the end of a catheter shaft 430 (as illustratedfor example in FIG. 4A). During ablation, some or all of the four pairsof ablation electrodes 436 may be activated simultaneously. For example,four lesions can be made simultaneously in a helical pattern along thewall of a lumen. Additionally, ablation current may be delivered betweenablation electrodes on adjacent spines, for example between electrodes436 b and 436 c, between electrodes 436 d and 436 e, etc.

In some embodiments, flow 439 in a lumen may help hold membrane 434 inan expanded configuration. For example, as shown in FIG. 4B, thedownstream (distal) opening 437 b of membrane 434 may be narrower thanthe upstream (proximal) opening 437 a. When placed inside an artery,downstream opening 437 b may present resistance against blood flow 439.Resistance to flow 439 exiting membrane 434 may cause pressure withinmembrane 434 to increase. Increased internal pressure may make membrane434 expand against an artery wall and/or spread out, for example like aparachute and/or a windsock.

FIG. 5 illustrates a tubular insulator 534 having a form of a windsockand/or a parachute deployed from a catheter 530 in accordance with someembodiments of the current invention. Optionally fluid may flow 539through a passageway 577 through insulator 534. For example fluid mayenter a large opening 537 a (illustrated for example at the proximal endof insulator 534). Optionally the fluid may exit a smaller opening 537 b(for example windows at the distal end of insulator 534). The dynamicpressure of the fluid flow 539 (for example blood flow in an artery) mayhelp keep the insulator 534 inflated. For example, fluid pressure maypress insulator 534 against walls of a lumen. Optionally, insulator 534and/or other structural members 532 may insulate electrodes 536 fromlumen fluids. Internal pressure may optionally be used to causeexpansion on its own or along with another mechanism. In someembodiments, pressure against an inner surface of a lumen may beaugmented by structural members. Some structural members may carry anelectrode. Alternatively or additionally some structural members that donot carry electrodes may be introduced for example to provide supportfor the insulator. For example, in the exemplary embodiment of FIGS. 6Aand 6B, a basket may be formed by cutting out from a nitinol tube. Thedeploying of the basket may optionally include supports springing out(where the direction of expansion has been determined by heat settingthe memory of the nitinol wire). FIG. 6A illustrates the basket in acollapsed configuration and FIG. 6B illustrates the basket in anexpanded configuration. Production of the tube and/or the cutting mayoptionally be similarly to production of a stent. The basket may includevarious structural elements, for example struts 632, cross members 633,support members 643, end members 647 and/or cantilever members 645.Supports 643 may for example retain a preferred geometry of otherstructural members and/or also provide a support for the geometry of theinsulator. Cantilever members may for example supply pressure on partsof the insulator.

In some embodiments, support for electrodes and/or an insulator may besupplied by a spiral wire basket. For example as shown in the exemplaryembodiment of FIG. 7 a spiral element 732 may be expanded by twisting inone direction 751 and/or collapsed by twisting in the oppositedirection. Optionally, an axial wire 753 may be used for twisting spiralelement 732. For example, spiral element 732 may be located at thedistal end of a catheter 730. Catheter 730 may include multiple spiralelements and/or other elements that may be expanded and/or collapsed toform a desired shape. The expanding elements may optionally cause aninsulating membrane to take a circular cross section and/or press aninsulating membrane against the walls of a lumen. The resulting shape ofthe membrane in an expanded configuration may depend on the way in whichthe spiral elements of the basket deploy. In some embodiments,electrodes and/or markers and/or an insulating frame and/or aninsulating membrane may be mounted and/or included on element 732.

In some embodiments, support members for an insulator may extend aroundan electrode, for example as illustrated in FIG. 8. Optionally, a strut832 may hold an electrode 836 and/or a frame 853 against a tissue to beablated. Frame 853 may optionally electrically insulate electrode 836and/or an area of tissue around electrode 836 from fluid in a lumen. Insome embodiments, frame 853 may conduct heat away from electrode 836and/or the tissue near electrode 836. For example, the heat may beconducted to a heat sink cooling electrode 836 and/or the tissue aroundelectrode 836.

FIGS. 9A-B, illustrate an insulating membrane 934 wrapped around asupport structure in accordance with some embodiments of the currentinvention. Electrodes 836 may optionally protrude through holes inmembrane 934 to contact the tissue. Frame 853 may hold membrane againstthe tissue around electrode 836 optionally insulating electrode 836 froma bodily fluid. Optionally, additional support members (for examplemembers 943) may supply further support to membrane 934. Alternativelyor additionally, frame 853 may be an insulator. In some embodiments maynot a surrounding membrane 934. Alternatively or additionally a nitinolstent type support structure may support electrodes 836 and/or a frame853 and/or a membrane 934. Exemplary nitinol stent type supportstructures are illustrated for in FIGS. 6 and 10.

FIG. 10 illustrates a nitinol support structure with a surroundingmembrane 934 and a frame 853 around electrodes 836 in accordance withsome embodiments of the current invention. Optionally, an ablationdevice (for example as illustrated in FIG. 8 and/or FIGS. 9A-B and/orFIG. 10) may include one or more markers for example similar to markers455 a,b.

In some embodiments, a ablation device may include a laminated membrane.For example as shown in FIGS. 11A-B, the membrane may be formed bylaminating several layers of polymers with similar and/or differentcharacteristics. Optionally, the laminated membrane may tend to expandoutwardly. For example, the laminated membrane may push outward againsta lumen wall, insulating the wall from fluid inside the lumen.

FIG. 11A illustrates a balloon 1134 a insulator in accordance with someembodiments of the current invention. In some embodiments, balloon 1134a may be fitted inside a support structure 1132. Optionally, supportstructure 1132 may include a stent type support (for example asillustrated in FIG. 6). As illustrated for example in FIG. 11B, balloon1134 a may be welded to the support structure 1132. For example, weldingmay be by adhering balloon 1134 a to a layer of polymer film 1134 b in alamination that sandwiches the support structure 1132 between the twolayers (balloon 1134 a and film 1134 b). Further layers may optionallybe added, for example to achieve a desired stiffness, elasticity,deformability, heat conductivity and/or electrical conductivity.

Optionally, the ends of the balloon may be trimmed and/or removed toproduce a tubular form and/or a passageway for fluid flow. Optionally,heat conducting elements may be introduced between the layers topreferentially cool particular areas of an ablation zone (for example aportion of the target tissue and/or an electrode).

In some embodiments, a braid of wires that forms a catheter shaft may beexpanded to form a basket support for an insulator. For example, spiralelement 732 of FIG. 7 may form part of a braided casing of a catheter.FIGS. 12A-B illustrate a catheter having braided elements in accordancewith some embodiments of the current invention. For example, the braidedelements may include one or more insolated Copper wires 1232 a (forexample copper with a polyimide insulation [Cu-Pi]) and/or one or morestainless steel [SST] wires 1232 b. Optionally, Cu-Pi wires 1232 a maybe used to carry current and/or signals between a control unit, a signalgenerator and/or an antenna in the catheter. The catheter may alsoinclude one or more axial wires 1232 c. The axial wires 1232 c may forexample be formed of Nitinol. For example, at a distal end of a catheterone or more nitinol wire 1232 c may form a support structure; forexample as illustrated in FIG. 12B. One or more Cu-Pi wire 1232 a maycarry a current and/or a signal between a signal generator and/or areceiver at a proximal end of the catheter and an electrode 1236 and/ora sensor and/or an electrode at a distal end of the catheter, forexample as illustrated in FIG. 12B. Alternatively or additionally anexpanding basket may be made of radial and/or spiral elements.Alternatively or additionally, a pull wire 1257 may be provided todeploy an expanding support structure. For example, in some embodiments,a guidewire tube may be used as a pull wire.

In some embodiments, the wires that form the basket may not be formed asa separate distal head to the catheter. Optionally, the wires that formthe basket may be part of the conductors that come all the way through acatheter's shaft 1230. For example, a conductor (for example bringingcurrent and/or a signal to or from an electrode) may be aninsulation-coated nitinol wire. The wire may provide structural support,for example forming a spline strut. The same wire may also serve as anelectrical conductor.

FIGS. 13A-C and FIGS. 14A-C illustrate embodiments of insulators andsupport structures formed as a malecot in accordance with someembodiments of the current invention. For example in FIGS. 13A-C tubinginside of a catheter expands out of slits in a malecot breakconfiguration. Alternatively or additionally in FIGS. 14A-C a malecotextends out a distal end of a catheter.

In some embodiments, for example as illustrated in FIGS. 13A-C acatheter may have malecot 1363 and/or a multi-lumen profile with wirebreakout slits 1359. FIG. 13A illustrates malecot 1363 in an expandedconfiguration in accordance with some embodiments of the presentinvention. At slits 1359 an outer sheath 1330 of the catheter may allowan inner tubing 1332 to expand into a basket shape during actuation.Conducting wires may optionally run through a lumen of tubing 1332.Electrodes 1336 and/or markers may be mounted on tubing 1332 and/orconnected to a signal generator and/or signal receiver via theconducting wires. An insulator may include a tubular membrane 1334surrounding sheath 1330 at the location of slits 1359. When malecot 1363expands it may be surrounded by membrane 1334. Membrane 1334 may haveopenings through which electrodes 1336 protrude to contact the tissue tobe ablated. FIG. 13B,C illustrate malecot 1363 in a retractedconfiguration. An inner lumen of the catheter may include a pull wire1357 that may be used to expand and/or retract malecot 1363. Alternatelyor additionally the insulator may include a frame mounted on tubing 1332surrounding electrodes 1336 for example similar to frame 853 of FIG. 8.Alternately or additionally an insulating membrane may surround tubing1332 on the inside of sheath 1330. When the malecot 1363 is expanded,the alternative membrane may expand out of slits 1359 in a star shape.

FIGS. 14A-C illustrate a malecot 1463 extending out of a distal end of acatheter in accordance with some embodiments of the current invention.Optionally malecot 1463 may be formed of a laser-cut Nitinol tube.Optionally malecot 1463 may have an retracted configuration where itfits in a catheter 1430 with an outer diameter of less than 2 mm and/oran extended configuration wherein malecot 1463 extends out of the distalend of catheter 1430. In some embodiments in the extended configurationmalecot may have a diameter of less than 3 mm. For example malecot 1463is illustrated in an extended configuration in FIGS. 14A and 14B. In theextended configuration struts 1432 of malecot 1463 may be slightlyexpanded. Optionally malecot 1463 may have an expanded configuration.For example, FIG. 14C illustrates malecot 1463 in an expandedconfiguration. For example, an axial compressing force (for exampleexerted by pulling a pull wire) may cause malecot 1463 to expandradially from the extended configuration to the expanded configuration.The degree of expansion and/or pressure on the tissue to be ablated mayoptionally be user controllable according to the tension on the pullcord. In the expanded configuration the diameter of malecot 1463 may belarger than the diameter in the extended configuration and less than forexample 7.5 mm. Malecot 1463 may carry electrodes 4136 and/or markers.Malecot 1463 may include an insulating sleeve for example similar tomembrane 1334 and/or an insulating frame (for example similar to frame854) for insulating electrodes 1336.

FIGS. 15A-B illustrate insulators for an ablation device that may beexpanded by hydraulic pressure in accordance with some embodiments ofthe current invention. For example, FIG. 15A illustrates an exemplarysupport structure including a hydraulic struts 1532 a. FIG. 15Billustrates an exemplary insulator for an ablation device including atube formed as a double hydraulic sleeve 1532 c which may be inflated byincreasing hydraulic pressure between the sleeves. Lumen fluids (forexample blood) may flow 1539 through a passageway in the inner sleeve.Struts 1532 a and or sleeve 1532 c may optionally carry electrodes 1536and/or an insulator (for example a membrane sleeve and/or a frame aroundelectrodes 1536 and/or wires 1532 b and/or markers.

Insulating sleeves and/or hydraulic sleeves may be constructed forexample by blow molding. Blow molding may optionally allow for securemounting of a membrane proximal and distal to an expandable support.

FIG. 16A-C illustrate a flexible circuit board ablation device inaccordance with some embodiments the present invention. For example aflexible printed circuit board (PCB) may be made of polyimide (PI).Circuits may optionally be printed on one or more surfaces. FIG. 16Aillustrates a flexible circuit board 1663 for an ablation device laidout flat, according to some embodiments of the present invention. Board1663 may include electrodes 1636 that may optionally be mounted onflexible struts 1632. The ablation device may optionally be connected toa support structure, for example a nitinol basked and/or an inflatablestrut. The ablation device may include connections to other devices forexample electrical leads and/or rings 1565 for connecting to structuralsupports and/or shaft transition pads 1667 through which electricalconnection is made between the printed circuit board and the wireswithin the catheter's shaft that transmit and/or receive energy to/froman RF generator and/or receiver. FIG. 16B illustrates circuit board 1663rolled up as a tube in a retracted configuration for mounting into acatheter. FIG. 16C illustrates a cross sectional view of an embodimentof board 1663 inserted in a body lumen 1669 in an expandedconfiguration. Electrodes 1636 may optionally contact with the innersurface of the walls of lumen 1669. Struts 1632 may optionally serve asan insulator. For example, the outer surface of struts 1632 may contactthe wall of lumen 1669 in an area surrounding electrodes 1636. Forexample, struts 1632 may prevent shunting of current from electrodes1636 to fluid inside of lumen 1669. Alternatively and/or additionally,struts 1632 may transfer heat from electrodes 1636 and or the wall oflumen 1669 to the lumen fluid. The lumen fluid may flow across the innersurface of struts 1632. For example the thickness and/or material ofstruts 1632 may be adjusted to achieve a desired conductivity and/orresistance to electrical current and/or heat flow. For example, a heatsink may be printed on board 1663 and/or a channel may be printed toconduct heat from one or more electrodes 1636 and/or tissue in contactwith board 1663 to a heat sink and/or lumen fluid. For example heat maybe conducted and/or absorbed by a high heat conductivity channel and/ora high heat capacity element such as a metal insert and or channel inthe insulator.

Optionally the geometry of a heat sink and/or heat conduction channelmay be adjusted to cool a particular area more than another area. Forexample, a highly heat conductive region may be formed near anelectrode, preferentially cooling an area near the electrode. Furtherfrom the electrode the heat conductivity may be smaller. Thus, coolingmay be increased near the electrode where overheating is more prevalent.

5 Control Unit

FIG. 17 illustrated a control unit for an ablation device in accordancewith some embodiments of the current invention. For example a controlunit may include one or more radio frequency (RF) channels 1776. Thecontrol unit may optionally have a number of channels 1776 that conveyelectrical signals for bipolar ablation between multiple electrode pairs(for example between specific pairs and/or any combination of a largenumber of electrodes, e.g., electrodes 436 a-h, electrodes 1336 etc.,mounted for example on a spine of the catheter's working end).Alternatively or additionally, RF channels 1776 may convey a signal forunipolarly ablation (for example between one or more ablation electrodese.g., electrodes 1336 and a dispersive electrode, e.g., electrode 440).In some embodiments the dispersive electrode may be located inside acatheter (for example a shaft electrode). For example, an internaldispersive electrode may be placed in contact with fluid (e.g. blood)inside a lumen (e.g. a blood vessel) wherein the ablation is takingplace.

In some embodiments, signal of a single frequency may be conveyed forone or more electrodes, e.g., to pair of electrodes in bipolar ablationor one or more electrodes in unipolar ablation). In some embodiments,signals of a plurality of frequencies may be conveyed for one or moreelectrodes. For example, in bipolar ablation: a first pair of electrodesmay receive signal of a first frequency and a second pair of electrodesmay receive signal of a second frequency. For example, in unipolarablation: a first electrode may receive signal of a first frequency anda second electrode may receive signal of a second frequency.

In some embodiments, a phase difference of the signal conveyed to a pairof electrodes may be controlled, e.g., by controller 1774. Optionally,the phase difference may be controlled based on impedance and/ortemperature measurements. In some embodiments, other parameters of asignal conveyed to one or more electrodes may be controlled, e.g., basedon impedance and/or temperature measurements.

Selecting electrodes may optionally be according to a switchconfiguration. The selection may optionally be set by a multiplexer1778. Optionally, RF channels 1776 may have the means to measureelectrode/tissue impedance under whatever selection is set by the switchconfiguration of the multiplexer 1778. The RF channels 1776, theswitches and/or multiplexor 1778 may be controlled by a centralcontroller 1774 (for example the central controller 1774 may include aprocessor, for example a microcontroller and/or single-board computer).The control unit may include receiver that is able to measuretemperature inside the lumen (for example by means of a thermocoupleattached at the location of one, some or all of the electrodes and/or atother locations). The control unit may include a user interface 1780,for example a graphical user interface (GUI), e.g. presented on a touchscreen.

In some embodiments, electrode impedance measurements may be used toestimate contact between electrode and tissue. Alternatively oradditionally impedance measurements may be used as surrogate for thermalcontact between electrode interface and target tissue. Optionally, RFpower, electrode temperature, and electrode impedance may be used toestimate power being converted to heat at electrode/tissue interface.The estimated contact and/or estimated power may optionally be used tocalculate energy transferred to target tissue and/or resulting targettissue temperature. Temperature and/or impedance measurements may beused in real-time to determine whether to apply unipolar or bipolarablation. Optionally, other sensors inputs may be used in real-time todetermine whether to apply unipolar or bipolar ablation. In someembodiments, the operator (e.g., a physician) may determine whether toapply unipolar or bipolar ablation, optionally based on temperatureand/or impedance measurements which may be displayed to the operator.Additionally or alternatively, temperature and/or impedance measurementsmay be used in real-time to control power and duration of ablation. Thepower and/or duration of ablation may optionally be used to ensurequality of lesion formation. The generator may estimate lesion qualityfor an individual electrode and/or for an area between electrodes. Thealgorithms may optionally alert a user that lesion formation has beencompleted when the quality of lesion at each electrode location reachesa predetermined range. The algorithm may change the electrodes beingpowered and/or the power level and/or frequency dependent on thedifferential progress of ablation. In some embodiments, the algorithmmay recommend changes to a use and wait for user input before makingchanges. For example, if ablation is progressing faster at a firstelectrode of a pair of electrodes than at a second electrode, thealgorithm may recommend switching to unipolar ablation at the secondelectrode and/or may automatically switch. For example, if ablation islocalized too much at the electrode locations, the algorithm mayrecommend changing to a frequency that penetrates tissue better.

In some embodiments, the control unit may measure complex bipolar and/orunipolar electrode impedance. For example impedance may be measured atthe ablation frequency and/or at another frequency. Optionally,measurements may be made while ablating based on the ablation signal.Alternatively or additionally, impedance measurements may be made whennot ablating. For example, during a interruption in ablation, impedancemay be measured using an auxiliary signal. The auxiliary signal may begenerated by an RF generator of one or more of channels 1776. Theauxiliary signal may optionally meet the requirements of an auxiliarycurrent not meant to cause any physiological effect. In someembodiments, electrode Impedance measurements shall be possible withinthe 100Ω to 1 kΩ range with a minimum accuracy of 5%, and within the1001Ω to 2 kΩ range with a minimum accuracy of 10%. Minimumrepeatability within the 100Ω to 2 kΩ range may optionally be 5%. Insome embodiments, ablation interruptions of less than 100 ms may be madefor measuring impedance during ablation segments. Optionally, anauxiliary signal for impedance measurements may have the same frequencyas ablation signals and/or an auxiliary signal for impedancemeasurements may have a different frequency from an ablation signal.Optionally, impedance measurements may be conveyed between a pair ofelectrodes being used for an ablation and/or an impedance measurementmay be conveyed between electrodes between which there is no currentablation treatment. For example, during an interruption in bipolarablation impedance may be measured between a disperse electrode and oneablation electrode of the active bipolar pair. Optionally, impedancemeasurements may be taken at a rate greater than 100 samples/s.

6 Evoked Response

In some embodiments, evoked response may be used for determining atreatment location and/or measuring ablation progress. For example acatheter may be supplied with an apparatus for measuringvasoconstriction (for example through balloon pressure, strain onsupports, pressure on a transducer [for example measuring blood pressurein the lumen being ablated and/or elsewhere], electrical signals [pickedup for example by an antenna and/or an electrode in the catheter orelsewhere] and/or impedance measurements, for example as illustrated inFIG. 20 and FIGS. 21A-B). Target sites may optionally be located byfinding regions where electrical stimulation delivered through theelectrodes causes a significant vasocontractile response. Once ablationis started, changes in vasocontractile response to stimulation may beused to control the delivery of energy until a certain dampening of thevasocontractile response indicates desired extent of the effect of theablation. Alternatively or additionally, the evoked electrical responseto stimulus may be measured to find ablation sites and/or to estimatethe extent of the effect of the ablation.

FIG. 18 illustrates an exemplary method of finding a receptor (forexample a receptor may include perivascular renal nerve) and/orascertaining ablation progress via evoked response, in accordance withsome embodiments of the invention. In some embodiments, a stimulationelectrode (which could include for example an ablation electrode) ispositioned 1844 at a location wherein there may be an ablation candidatereceptor and the tissue may be stimulated 1846 for example via anelectrical signal. The response may be measured 1848 (for example thevasoconstriction and/or the electrical response). For example, a fastand/or strong response may indicate the presence of a receptor. If areceptor is not found 1850, then the simulation electrode is positioned1844 at a new location. If a receptor is found 1850, then the ablation1813 may proceed. Ablation 1813 may include bipolar ablation (forexample bipolar ablation 112 as described hereinabove) and/or unipolarablation (for example unipolar ablation 114 as described hereinabove).In place of and/or in addition to the tests described herein aboveevoked response may be used to measure ablation progress. Duringablation, current application may be interrupted and an electricalsignal may be transmitted to stimulate 1852 the tissue. The evokedresponse to stimulation may then be measured 1854 (for example thevasoconstriction and/or the electrical response). If the response is notyet damped 1856 enough, then ablation 1813 may continue. If the responseis damped 1856 enough, then the process ends (for example either theablation session ends and/or the process restarts finding another siteand optionally ablating that site).

In some embodiments, the method illustrated in FIG. 18 may be used fordetermining a treatment location in a body of a treated patient e.g., bystimulating a tissue and detecting the elicited vasocontractileresponse. Treatment locations may be located by finding regions whereelectrical stimulation delivered through the electrodes causes asignificant vasocontractile response. Once ablation is started, changesin vasocontractile response to stimulation may be used to control thedelivery of energy for example until a certain dampening of thevasocontractile response indicates desired extent of lesion formation.Optionally, the evoked response may be measured in the intravascularspace (for example by a blood pressure sensor in the catheter) and/orelsewhere in the body (for example through a blood pressure or bloodflow sensor elsewhere in the body and/or from a location external to thebody, for example through a blood pressure sensor, heart rate sensor, orplethysmography sensor).

In some embodiments, an evoked response may include an electricalreaction signal produced in response to a stimulus. Optionally, thestimulus may be applied inside a lumen of the patient, for example by adevice on the ablation catheter. Optionally, a target site may beidentified as a region where delivering a stimulation causes asignificant evoked response. For example, a target for ablation mayinclude a nerve terminal. Optionally, the stimulus may include anelectrical signal. The evoked response may be measured for example as anelectrogram. Optionally, the evoked response may be measured in theintravascular space (for example by electrodes of the catheter) and/orelsewhere in the body (for example at a nerve location elsewhere in thebody and/or external to the body (for example using an externalelectrode). Once ablation is started, changes in evoked response tostimulation may optionally be used to control the delivery of energyuntil a certain dampening of the evoked response is detected. Thedampened response may optionally indicate a desired extent of lesionformation. When sufficient dampening is detected, ablation mayoptionally be stopped.

FIG. 19 illustrates an exemplary stimulation and evoked response, inaccordance with some embodiments of the invention. For example, curve1961 a illustrates a stimulation to the receptors before ablation(either while searching for receptors or at the beginning of ablation).The abscissa shows time (for example a few milliseconds) and theordinate may include for example the voltage of the signal and/or thecurrent. The measured return signal is represented by graph 1962. Themeasured signal may include a change in pressure in a balloon due tovasoconstriction and/or a stress and/or a strain on a support of abasket (for example support 432) and/or a change electrical potentialand/or impedance measured on the tissue. For example, curve 1961 billustrates a stimulation to the receptors after ablation. For example,curve 1964 illustrates the dampening of the return signal aftersuccessful ablation.

FIG. 20 illustrates an ablation device 2000 capable of measuring evokedresponse in accordance with some embodiments of the current invention.Ablation device 2000 may, for example, include a support structuresimilar to that of FIG. 4C (for example including struts 432). Ablationdevice 2000 may option include markers (for example similar to markers455 a,b—not illustrated), electrodes 436, an insulator (for example amembrane 434) and/or other components or structures described above. Forexample, the support structure, markers, electrodes 436 and/or insulatormay be similar to one, some and/or any of the embodiments above.Optionally, ablation device 2000 may include one or more sensors tosense evoked response. For example, a strain gauge 2070 may measureevoked vasoconstriction response and/or resultant squeezing of thesupport structure. Alternately or additionally, ablation device 2000 mayinclude a pressure transducer to measure the fluid pressure inside alumen. Ablation device 2000 may include exemplary thermocouples 2072 formeasuring temperature near the ablation electrodes 436.

FIGS. 21A-B illustrate a perspective and a cross sectional viewrespectively of an alternate ablation device 2100 capable of measuringevoked response in accordance with some embodiments of the invention.Ablation device 2100 may, for example, include a malecot supportstructure similar to that of FIGS. 14A-C (for example including struts1432). Ablation device may option include markers (for example similarto markers 455 a,b—not illustrated), electrodes 1336 and/or an insulator2134. Ablation device 2100 may include other components or structuresdescribed above. For example, the support structure, markers, sensors,electrodes sensors and/or insulator may be similar to one, some and/orany of the embodiments above. Optionally, ablation device 2100 may beconfigured to sense evoked response. For example, insulator may beconfigured to sense pressure and/or shape changes caused by evokedvasoconstriction response and/or resultant squeezing of the supportstructure. For example, insulator 2134 may include an internal liquidfilled cavity 2179. Changes in the shape of insulator 2134 may inducechanges in the internal pressure in cavity 2179 and may be sensed by apressure transducer. Alternately or additionally, ablation device 2100may be constructed of multiple layers of material which may produce anelectrical response (for example a change in resistance) under strain.The electrical response may be sensed and/or used detect an evokedresponse. The materials of insulator 2134 and or the fluid betweenlayers may be chosen to provide a heat sink and/or heat conductor, forexample for conducting heat away from the ablation zone. Insulator 2134may include a central passageway 2177 through which lumen fluids mayflow 2139. Optionally, struts 1432 may pass through support lumens 2175in insulator 2134.

It is expected that during the life of a patent maturing from thisapplication many relevant technologies will be developed and the scopeof the terms used herein is intended to include all such newtechnologies a priori. As used herein the term “about” refers to ±10%.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, pharmacological, biological,biochemical and medical arts.

As used herein, the term “treating” includes abrogating, substantiallyinhibiting, slowing or reversing the progression of a condition,substantially ameliorating clinical or aesthetical symptoms of acondition or substantially preventing the appearance of clinical oraesthetical symptoms of a condition.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

1. (canceled)
 2. The ablation catheter of claim 39 wherein, saidinsulator is a radially expanding tubular insulator sized and shaped tofit in a lumen of a blood vessel in an expanded configuration.
 3. Theablation catheter of claim 2, wherein an inner passageway of saidradially expanding insulator expands toward walls of said lumen byplastic deformation of said radially expanding insulator.
 4. (canceled)5. The ablation catheter of claim 39, wherein said insulator isconfigured to contact an area of an inner surface of said walls of thelumen surrounding at least one of said at least one ablation electrode.6. (canceled)
 7. The ablation catheter of any of claim 39, wherein saidat least one ablation electrode includes at least four pairs of ablationelectrodes.
 8. The ablation catheter of claim 7 further comprising: acontrol unit selectively conveying an ablation signal between electrodesof each of said at least four pairs of ablation electrodes.
 9. Theablation catheter of claim 7, wherein said at least four pairs ofablation electrodes are helically distributed around said insulator.10-14. (canceled)
 15. The ablation catheter according to claim 39,wherein said area of said tissue surrounding said electrode includes amargin of at least 3 mm surrounding said at least one electrode. 16-27.(canceled)
 28. An ablation catheter comprising: a plurality of ablationelectrodes configured to be in contact with a target tissue in a lumen;a dispersive electrode configured to be provided in the lumen, thedispersive electrode having a conducting contact area at least 20 timesas large as the ablation electrode; and a control unit conveying: afirst signal between a pair of said plurality of ablation electrodes;and a second signal between said dispersive electrode and at least oneof said plurality of ablation electrodes.
 29. The ablation catheter ofclaim 28, further comprising: an insulator electrically insulating atleast one of the plurality of ablation electrodes from a fluid in saidlumen.
 30. (canceled)
 31. The ablation catheter according to claim 28,configured to define a passageway for a fluid to pass through the lumen.32. The ablation catheter according to claim 29, wherein a first side ofthe insulator is in contact with the target tissue in a vicinity of saidablation electrode and a second side of the insulator is in contact withfluid when the fluid is in a passageway and heat transfer to said fluidacross said insulator cools said target tissue in said vicinity of saidablation electrode.
 33. The ablation catheter according to claim 28,wherein the dispersive electrode is in contact with a fluid inside saidlumen.
 34. A method of ablation therapy inside a lumen of a patientcomprising: positioning a plurality of ablation electrodes in contactwith a target tissue in said lumen; conveying through said target tissuea first electrical signal between a pair of said ablation electrodes;conveying through said target tissue a second electrical signal betweenat least one of said plurality of ablation electrodes and a dispersiveelectrode having an active surface area at least twenty times an activesurface area of said ablation electrode; and placing at least a portionof said dispersive electrode in said lumen.
 35. The method of claim 34,wherein the plurality of ablation electrodes form part of a cathetercomprising an expandable insulator insulating electrically at least oneof said ablation electrodes from fluid in said lumen.
 36. The method ofclaim 34, further comprising: contacting said dispersive electrode withfluid in said lumen.
 37. (canceled)
 38. The method of claim 34, whereinsaid placing is by means of a catheter.
 39. An ablation cathetercomprising: at least one ablation electrode in contact with a tissue onan inner wall of a lumen; an insulator including: a tissue side incontact with an area of said tissue surrounding said electrode; and alumen side in contact with fluid in the lumen, the insulatorelectrically insulating the at least one ablation electrode from a fluidin the lumen and cooling said at least one ablation electrode byconducting heat to said fluid in the lumen; and a passageway allowingfluid flow through the lumen.